Cartridge type hydraulic valves typically have a cylindrical sleeve inserted into a bore of a valve body to control fluid flow through several passages opening into the bore. Seals are commonly disposed in annular grooves formed in the sleeve to isolate the passages from each other. One type of seal used in such applications is called an "O" ring and is made from a resilient elastomeric material. One of the problems encountered is that sharp edges are generated where the passages open into the bore and the elastomeric seals are susceptible to cuts and/or abrasion as they pass by the passages during assembly. To prevent damage to the seals during assembly, the valve body is sometimes provided with a stepped bore to minimize the number of times that the seal must pass by the opening of the passages into the bore. However the stepped bore takes up more space, increases sleeve and valve body stresses and is more costly to machine.
Some of the newer cartridge valves use sleeves made from a different material than the valve body. For example the body may be made from a metallic material and the sleeve made from plastic. To prevent distortion of the sleeve due to the differences in thermal expansion, the size of an annular gap existing between the sleeve and the bore is increased. A problem encountered therewith is that the elastomeric "O" ring can be extruded into the larger gap by pressurized fluid. This problem has been minimized somewhat by using a two piece seal assembly consisting of a plastic seal element and an elastomeric energizer which resiliently biases the plastic seal into contact with the bore surface. However the two piece seals are more difficult to assemble properly and have a larger profile that requires a deeper or wider annular groove formed in the sleeve. The larger groove in the sleeve increases the stress concentration in the sleeve which often results in a larger cartridge valve.
Thus it would be desirable to have a one piece seal which is self-energizing to cause initial sealing between the seal, the bore surface and the annular groove and which is made from a material having sufficient rigidity to permit the seal to pass by an edge many times without being cut or abraded and to prevent extrusion into the annular gap between the sleeve and bore while having sufficient resilience to permit assembly into the groove and to compensate for thermal expansion differences between the sleeve and the valve body.
The present invention is directed to overcoming one or more of the problems set forth above.